Conductive organic-inorganic hybrid material comprising a mesoporous phase, membrane, electrode and fuel cell

ABSTRACT

A conductive organic-inorganic hybrid material comprising a mineral phase in which walls define pores forming a structured mesoporous network with open porosity; said material further comprising an organic oligomer or polymer integrated in said walls and bonded covalently to the mineral phase, and optionally another phase inside the pores, composed of at least one surfactant; at least one of the mineral phase, the oligomer, and the organic polymer having conductive and/or hydrophilic functions. Membrane and electrode comprising this material. Fuel cell comprising at least one such membrane and/or at least one such electrode. Process for preparing said material.

The present invention concerns a conductive organic-inorganic hybridmaterial comprising a mesoporous mineral phase.

The invention additionally concerns a membrane and an electrodecomprising said material.

The invention likewise pertains to a fuel cell comprising at least onesuch membrane and/or at least one such electrode.

The invention relates, finally, to a process for preparing theorganic-inorganic hybrid material.

The technical field of the invention may be defined, generally speaking,as being that of porous materials and more particularly of materialsreferred to as mesoporous.

More specifically the invention is situated within the field ofmesoporous materials intended for use in electrochemistry, in particularin fuel cells, such as those of (PEMFC) (polymeric electrolyte membranefuel cell) type.

It is known that one of the essential elements of fuel cells—forexample, those used in the automotive sector and in the mobile telephonysector—is the proton exchange membrane.

These membranes structure the core of the fuel cell and are consequentlyrequired to exhibit good proton conduction performance and a lowpermeability to the reactant gases (H₂/O₂). The properties of thematerials which constitute the solid polymer electrolytes forming thesemembranes, and which are required to withstand thousands of hours ofoperation of the cell, are essentially chemical stability and resistanceto hydrolysis and to oxidation, especially hydrothermal resistance, anda certain mechanical flexibility.

Membranes prepared from perfluorinated ionomers, particularly Nafion®,meet these requirements for operating temperatures below 90° C.

This temperature, however, is insufficient to allow the integration offuel cells comprising such membranes in a vehicle. This is because suchintegration presupposes an increase in the operating temperature to100-150° C. with the aim of increasing the current/energy conversionyield and hence the efficacy of the fuel cell, but also of improving thecontrol of heat management by reducing the volume of the radiator.

Furthermore, the conductive efficiency of proton membranes is stronglylinked to the presence of water in the medium. At temperatures greaterthan 100° C., water is rapidly evacuated from the membrane, theconductivity falls, and the fuel permeability goes up. At thesetemperatures, this decrease in performance may be accompanied bydegradation of the membrane. In order to solve the problems of membranedryout in fuel cells at high temperature, namely at least 100° C., themaintenance of a maximum, 80-100% relative humidity is necessary, but isdifficult to realize by means of an external source.

On the other hand, it is known that the insertion or growth of ahygroscopic filler “in situ” promotes the retention of water within thepolymer, retards this process of dehydration of the proton medium, andthus ensures the conduction of protons. Besides it hydrophilic nature,this functional filler may intrinsically possess conductive propertiesand may thus increase the performance of the membrane.

In order to increase the retention of water in the membranes in fuelcells at high temperature, numerous composite membranes have beendeveloped, in particular by growth of hydrophilic inorganicnanoparticles. These mineral nanofillers can be synthesized by a sol-gelroute in perfluorinated sulfonated organic matrices, but also inmatrices composed of polyaromatic compounds, or of polyethers. Thesemembranes are presently called organic-inorganic hybrid membranes.

The mineral particles may be:

conductive, in which case they are of acidic type, such as, for example,tungstophosphoric or tungstosilicic or antimonic acid, or of metalphosphate or phosphonate type, such as zirconium phosphate [1-7];

nonconductive and simply hydrophilic, such as metal and metalloid oxidesTiO₂, SiO₂ etc. [8-19].

Besides improving the water management at high temperature, thereduction of the permeability of the membrane with respect to fuels isdemonstrated in these organic-inorganic hybrid membranes relative, forexample, to conventional membranes of Nafion® type. The thermal andchemical stability, however, remain limited since they are inherent inthe sulfonated organic polymer matrix employed.

Studies presented recently by Rozière et al. [19] pertain to thefunctionalization of the silicate network by an amine group, whichimproves the interaction between the inorganic phase and the organicpolymer via ionocovalent bonds.

Research conducted by Honma et al. [20-21] and Park et al. [22] on thegrowth of continuous organic-inorganic hybrid matrices by dispersion ofheteropolyacids respectively inpoly(isocyanopropyl)silsesquioxane-organic polymer (PEG, PPO, PTMO)copolymers or in cocondensates of glycidyloxy-propyltrimethoxysilane(GLYMO) and tetraethoxysilane is opening up new perspectives on the useof thermally stable polymeric chains.

Although mineral heteropolyacids remain highly attractive on account oftheir intrinsic conductivity, their incorporation at high filler levels(30% to 70% by mass) into polymers with low or no conductivity givesrise generally to problems of consequent and progressive leaching duringthe operation of the cell, owing to their solubility in water.

In parallel with the composite or organic-inorganic hybrid materialsdescribed above, mesoporous materials, which were initially envisionedfor catalysis, in other words, essentially silica and aluminosilicates,have begun to attract the attention of certain electrochemists.

It will be recalled that materials referred to as mesoporous are solidswhich within their structure have pores possessing a size of typicallybetween 2 and 80 nm, which is intermediate between that of microporesand that of macropores.

Typically, mesoporous materials are amorphous or crystalline metaloxides in which the pores are generally distributed randomly with a verybroad distribution in the size of the pores.

Structured mesoporous materials, called “mesostructured” materials,correspond, for their part, to structured pore networks which exhibit anorganized spatial layout of mesopores. This spatial periodicity of thepores is characterized by the appearance of at least one low-angle peakin an X-ray scattering diagram; this peak is associated with a repeatdistance which is generally between 2 and 50 nm. The nanostructure isverified by transmission electron microscopy.

In this context, the sol-gel process offers innovative strategies in theconstruction of these organized mesoporous edifices, particularly byinorganic polymerization within organized molecular systems (OMS) ofsurfactants or within organized polymeric systems (OPS) of blockcopolymers. In the presence of OMS-type templating agents, this gentlechemistry also makes it possible, starting from inorganic andorganometallic precursors, to synthesize organic-mineral-typemesostructured networks of a kind referred to as organic-inorganichybrid materials. The properties of these mesoporous organic-inorganichybrid materials depend not only on the chemical nature of the organicand inorganic components but also on the synergy which may appearbetween these two chemistries.

This is why these materials are often called “multifunctional”materials.

The degree of organization is governed by the nature of these twoorganic and inorganic entities but also by the multiscale layout of thisarrangement. Thus, the integration into an ordered mesoporous structure,into both the “walls” and the pores, of chemical functionalities capableof inducing specific properties is of great interest in a variety ofapplications (catalysis, filtration, electrochemistry, etc.) [37].

Colomer et al. [23-24] have prepared nonorganized mesoporous silicas bycoaggregating silica nanoparticles of different sizes or by(pH-)controlled growth of colloidal silica. They have studied the impactof such porosities on the proton conductivity of these silicas in acidicmedium for PEMFCs. The high heat treatment at around 500-700° C. whichis necessary to generate the porosity and the consolidation of themesoporous silica nevertheless limits this technique to purely inorganicnetworks.

In contrast, the structuring of mesoporous silica synthesized by usingsurface-active agents does not require a high heat treatment and hencepermits organic functionalization during the growth of the network [25].Moreover, the structure of these materials is often well defined. Thisorganization, in association with the high specific surface area, playsan important part in improving the conduction of protons through thehydrophilic network. Minami et al. [26-28] have impregnated this type ofsilica with sulfuric or phosphoric acid, studying the influence of thepore size and of the specific surface area on conductivity and porosity.The properties obtained in terms of conductivity are of very greatinterest, being of the order of 2-3-10⁻¹ S/cm.

Moreover, different mesostructured organic-inorganic hybrid silicas,possessing an SO₃H [29-31] or PO₃H₂ [32] functionality in the pores,offer an interesting potential for fuel cells, despite having beenessentially developed for catalytic applications. Kaliaguine et al.[33], who work in the electrochemical field, have carried outconductivity and water-adsorption measurements in this type of compound.These silicas exhibit in the round a pronounced hydrophilic character,and the conductivity measurements are of interest for non-optimizedsystems, being of the order of 10⁻² S/cm at 80° C. and 100% relativehumidity.

The recent literature references above concerning the possible use ofmesoporous materials in electrochemical devices, such as themesostructured mesoporous silicas constructed by OMS and OPS, are unableto give rise to a direct application for fuel cells, because it isimpossible to convert the materials as described and mentioned in thosedocuments into the form of membranes.

A number of articles relate to the integration of a polymeric organicchain bonded covalently to the oxide and integrated in the walls of themesoporous network. In particular, Wei et al. [34] have synthesized amesoporous organic-inorganic hybrid material of polystyrene-SiO₂ typefrom a silylated polymer and TEOS in the presence of a surface-activeagent, dibenzoyltartaric acid. Other authors, such as Loy et al. [35] orStein et al. [36], have described the construction of a mesostructuredsilicate network whose walls contain integrated ethylene chains of 1 to4 units. Again, these materials cannot be formed as membranes and arenot possessed of any conductivity.

There exists, therefore, a need for a mesoporous material which can beconverted into the form of a membrane, in particular a homogeneous andflexible membrane.

There also exists a need for a mesoporous material which is thermallyand chemically stable and resistant to hydrolysis and to oxidation.

There subsequently exists a need for a mesoporous material of this kindwhich in addition can be provided with a high conductivity, inparticular a high ion—preferably proton—conductivity, and which can thusbe employed in membrane form in electrochemical devices, such as fuelcells, having high operating temperatures, in the region, for example,of 100 to 150° C.

This material, in the context of such a use, must allow—unlike themembranes of the prior art, based for example on perfluorinatedionomers—a high level of water retention, even at high temperature, inorder to avoid membrane dryout, and must possess a high conductivity anda low fuel permeability at high temperature, in association with anabsence of degradation of the membrane.

The aim of the present invention is to provide a mesoporousorganic-inorganic hybrid material which meets all of the needs indicatedabove.

The aim of the present invention is, further, to provide a mesoporousmaterial which does not exhibit the disadvantages, defects and drawbacksof the prior-art materials and which, if equipped with conductivefunctions, can be used in an electrochemical device, such as a fuelcell, while exhibiting excellent performance.

This aim and other, further aims are attained in accordance with theinvention by a conductive organic-inorganic hybrid material comprising amineral phase in which walls define pores forming a structuredmesoporous network with open porosity; said material further comprisingan organic oligomer or polymer integrated in said walls and bondedcovalently to the mineral phase, and optionally another phase inside thepores, composed of at least one surface active agent; at least one ofthe mineral phase, and the organic oligomer or polymer having conductiveand/or hydrophilic functions.

The specific structure of the conductive hybrid material according tothe invention, which comprises at least one mesoporous mineral phase(with, optionally, a surface active phase), whose mechanical strength isensured by an organic polymeric chain integrated in the walls of themesoporous network, has never been described in the prior art.

This is because the prior art has never documented the formation of amesoporous organic-inorganic hybrid material—in the form, for example,of a membrane—which is continuous and contains integrated polymer, saidmaterial further having conductive and/or hydrophilic functions, in thepores, for example.

In particular, by virtue of their high specific surface area and theirparticular structure, the use of such conductive organic-inorganichybrid materials comprising a mesoporous phase in proton conductivemembranes offers numerous possibilities promoting the continuity ofconduction pathways subject to the presence of an open porosity.

By open porosity is meant a porosity formed from pores which open outand remain accessible to the conductive species.

According to the invention, at least one of the mineral phase and theorganic oligomer or polymer has conductive and/or hydrophilic functions.

The mineral phase may thus have conductive and/or hydrophilic functionson the surfaces of its pores.

Similarly, the organic oligomer or polymer may have conductive and/orhydrophilic functions.

In one embodiment the other, optional phase inside the pores, composedof at least one surface active agent, may also, optionally, haveconductive and/or hydrophilic functions; it being understood that themineral phase and/or the organic oligomer or polymer compulsory hasconductive and/or hydrophilic functions.

By conductive functions it is meant, generally, that these functionsexhibit an ion conductivity, preferably a proton conductivity.

Where the material solely comprises a mineral phase and an organicoligomer or polymer, one or the other of them, or both, may haveconductive and/or hydrophilic functions.

Where the material further comprises a surface active agent, at leastone of the mineral phase and the organic oligomer or polymer hasconductive and/or hydrophilic functions, or else any two of the mineralphase, the organic oligomer or polymer, and the surface active agenthave conductive and/or hydrophilic functions, or else the surface activeagent and the mineral phase and the organic oligomer or polymer allthree have conductive and/or hydrophilic functions.

Generally speaking, the material according to the invention has an openporosity serving as a continuous network of proton conduction. Themesoporous skeleton is preferably hygroscopic and possesses a conductivefunctionality in its pores (the compound in question is, for example, afunctionalized metal oxide) which thus ensures proton transport andhydration. The organic polymer or oligomer reinforces the walls of themineral phase and provides it with structure, thereby allowing theconductive material, in contrast to the prior art, to be brought intothe form of a membrane.

A true synergy is produced between the mineral phase and the organicoligomer or polymer, which endows the material according to theinvention with a unique combination of physical, electrical, andmechanical properties, never attained in the prior art.

The conductive functions may be selected from cation exchange groupsand/or anion exchange groups.

The cation exchange groups may be selected, for example, from thefollowing groups: —SO₃M; —PO₃M₂; —COOM and —B(OM)₂, where M representshydrogen, a monovalent metal cation, or ⁺NR¹ ₄, where each R¹,independently, represents a hydrogen, an alkyl radical or an arylradical.

The anion exchange groups may be selected for example from the followinggroups: pyridyl; imidazolyl; pyrazolyl; triazolyl; the radicals offormula ⁺NR² ₃X⁻, where X represents an anion such as, for example, F,Cl, Br, I, NO₃, SO₄H, or OR (where R represents an alkyl radical or anaryl radical), and where each R², independently, represents a hydrogen,an alkyl radical or an aryl radical; and the basic aromatic ornonaromatic radicals containing at least one radical selected fromimidazole, vinylimidazole, pyrazole, oxazole, carbazole, indole,isoindole, dihydrooxazole, isoxazole, thiazole, benzothiazole,isothiazole, benzimidazole, indazole, 4,5-dihydropyrazole,1,2,3-oxadiazole, furazan, 1,2,3-thiadiazole, 1,2,4-thiadiazole,1,2,3-benzotriazole, 1,2,4-triazole, tetrazole, pyrrole, aniline,pyrrolidine, and pyrazole radicals.

The mineral phase is generally composed of at least one oxide selectedfrom metal oxides, metalloid oxides and mixed oxides thereof.

Said oxide is generally selected from the oxides of silicon, titanium,zirconium, hafnium, aluminum, tantalum, tin, rare earths or lanthanidessuch as europium, cerium, lanthanum or gadolinium, and mixed oxidesthereof.

The mineral phase of the material according to the invention is amesostructured phase, which means, more specifically, that themesoporous network exhibits an organized structure with a repeatingunit.

For example, the mesoporous network may exhibit a cubic, hexagonal,lamellar, vermicular, vesicular or bicontinuous structure.

The size of the pores of the mesoporous network is generally from 1 to100 nm, preferably from 1 to 50 nm.

The oligomer or the organic polymer integrated in the walls of themineral phase must generally meet a certain number of conditions.

Above all, said oligomer or said polymer must generally be thermallystable; by thermally stable is meant that it retains its propertiesunder the action of heat.

The polymer or the oligomer must generally, furthermore, not besensitive to hydrolysis and to oxidation at, in particular, hightemperatures, especially at the operating temperatures of fuel cells,and must retain this insensitivity for several thousand hours.

Moreover, generally, the polymer or the oligomer selected must be:

soluble in an alcoholic or aqueous-alcoholic medium or in other solventsthat are miscible or partly miscible in water, because the organizationof the optional surfactant in a liquid medium, the templating agent ofthe mesoporous phase, occurs in highly polar media such as water;

plastic, so as to provide sufficient strength to the mesoporousinorganic phase and form a self-supporting film: that is to say that thepolymer may be termed a (mechanically) structuring polymer.

The oligomer or the organic polymer will be generally selected frompolyetherketones (PEK, PEEK, PEEKK); polysulfones (PSU), Udel® forexample; poly-ethersulfones, Vitrex® for example;polyphenyl-ethersulfones (PPSU), Radel® for example; styrene/ethylene(SES), styrene/butadiene (SBS) and styrene/isoprene (SIS) copolymers,Kraton® for example; polyphenylenes, such as poly(phenylene sulfide)sand poly(phenylene oxide)s; polyimidazoles, such as polybenzimidazoles(PBI); polyimides (PI); polyamideimides (PAI); polyanilines;polypyrroles; polysulfonamides; polypyrazoles, such aspolybenzopyrazoles; polyoxazoles, such as polybenzoxazoles; polyethers,such as poly(tetramethylene oxide)s and poly(hexamethylene oxide)s;poly((meth)acrylic acid)s; polyacrylamides; polyvinyls, such aspoly(vinyl ester)s, for example, polyvinyl acetates, polyvinyl formates,polyvinyl propionates, polyvinyl laurates, polyvinyl palmitates,polyvinyl stearates, polyvinyl trimethylacetates, polyvinylchloroacetates, polyvinyl trichloroacetates, polyvinyltrifluoroacetates, polyvinyl benzoates, polyvinyl pivalates, andpolyvinyl alcohols; acetal resins, such as polyvinyl butyrals;polyvinylpyridines; polyvinylpyrrolidones; polyolefins, such aspolyethylenes, polypropylenes, and polyisobutylenes; poly(styreneoxide)s; fluoro resins and polyperfluorocarbons, such aspolytetrafluoroethylenes (PTFE), for example, Teflon®; poly(vinylidenefluoride)s (PVDF); polychlorotrifluoroethylenes (PCTFE);polyhexafluoropropenes (HFP); perfluoroalkoxides (PFA);polyphosphazenes; silicone elastomers; and block copolymers comprisingat least one block composed of a polymer selected from the abovepolymers.

When the material comprises a third phase, inside the pores, composed ofa surface active agent, the latter may be selected from: surfactants,such as alkyltrimethylammonium salts, alkyl phosphate salts andalkylsulfonate salts; acids such as dibenzoyltartaric acid, maleic acidor long-chain fatty acids; bases such as urea or long-chain amines;phospholipids; doubly hydrophilic copolymers whose amphiphilicity isgenerated in situ by interaction with a substrate; and amphiphilicmultiblock copolymers comprising at least one hydrophobic block incombination with at least one hydrophilic block. Among these polymersmention may be made, for example, of Pluronics® based on PEO(poly(ethylene oxide)) and PPO (poly(propylene oxide)), of(EO)_(n)—(PO)_(m)—(EO)_(n) type, copolymers of((EO)_(n)—(PO)_(m))_(x)—NCH₂CH₂N—((EO)_(n)—(PO)_(m))_(x) type(Tetronic®), the class C_(n)(EO)_(m)(OH) (C_(n)=aryl and/or alkyl chain,EO=ethylene oxide chain), for example, Brij, Triton or Igepal®, and theclass (EO)_(m)-sorbitan-C_(n) (Tween®).

It is important to note that the organic polymer or oligomer must in nocase be confused with an optional surface active polymer. Although bothcalled “polymers”, these compounds are different in terms both of theirstructure and of their effects. The organic oligomer or polymerintegrated in the walls is a polymer termed (mechanically)“structuring”, whereas the optional surface active polymer is termed“templating” “texturizing”.

The invention concerns, moreover, a membrane comprising the material asdescribed above, optionally deposited on a support.

By membrane is meant that the material is in the form of a film or sheetwith a thickness, for example, of 50 nm to several millimeters,preferably from 10 to 500 μm.

The invention also pertains to an electrode comprising the material, asdescribed above.

The excellent properties of the material according to the invention, inthe form of a membrane and/or an electrode, make it particularlysuitable for use in an electrochemical device, a fuel cell for example.

The invention therefore likewise concerns a fuel cell comprising atleast one membrane and/or electrode as described above.

The invention likewise pertains to a process for preparing the materialsuch as described above, in which the following steps are realized:

a)—a precursor compound A is synthesized, composed of an organicoligomer or polymer which carries precursor functions of the mesoporousmineral phase, and an organic-inorganic hybrid solution is prepared in asolvent of said precursor compound A;

b)—the organic-inorganic hybrid solution obtained in step a) ishydrolyzed and allowed to age;

-   -   c)—the hydrolyzed and aged organic-inorganic hybrid solution of        the precursor compound A, obtained in step b), is diluted in a        solution, in a solvent, of a mineral precursor B intended to        constitute the mesoporous mineral phase, whereby a new        organic-inorganic hybrid solution is obtained;

d)—the organic-inorganic hybrid solution obtained in step c) ishydrolyzed and allowed to age;

-   -   e)—a solution is prepared, in a solvent, of a surface active        agent D, a templating, texturizing, agent for the mesoporous        mineral phase;

f)—the solution obtained in step c) is mixed with the solution obtainedin step e) to give a solution S;

g)—optionally, the solution S obtained in step f) is hydrolyzed andallowed to age;

h)—the hydrolyzed and aged hybrid solution S is deposited or impregnatedon a support;

i)—solvents are evaporated under controlled pressure, temperature, andhumidity conditions;

j)—a heat treatment is carried out to consolidate the material;

k)—the surface active agent D is optionally removed completely orpartially;

l)—the support is separated or removed, optionally.

It should be noted that, when the material prepared is in the form, inparticular, of a thin film, or layer, and when it is deposited orimpregnated on a substrate, a planar substrate, for example, the processmay be defined as being a process for preparing a membrane.

The process according to the invention exhibits a unique sequence ofspecific steps which allow appropriate growth by the “sol-gel” route ofthe optionally functionalized mesoporous inorganic (mineral) phase inthe pores and containing, integrated in its walls, an organic polymer oroligomer. The conditions of the process ensure that a material isobtained, and then that a homogeneous and flexible membrane is obtained,coupled with the construction of the mesoporosity.

By virtue of the process according to the invention, the growth of themesoporous phase optionally functionalized in its pores and containing,integrated in its walls, an organic polymer or oligomer is perfectlycontrolled, especially in the presence of a templating, texturizing,surface active agent.

Advantageously, a chelating agent E is further added to the solution Sobtained in step f).

Advantageously, during step c), a compound C, carrying, on the one hand,conductive and/or hydrophilic functions and/or functions which areprecursors of conductive and/or hydrophilic functions, and, on the otherhand, functions capable of undergoing bonding to the surfaces of thepores of the mesoporous network, is further added to the solution ofmineral precursor A. Advantageously, the process further comprises afinal step of treatment to liberate or generate conductive and/orhydrophilic functions on the surface of the pores of the material.

Advantageously, the organic-inorganic hybrid solution obtained in stepa) (step b)) is left to age at a temperature of 0° C. to 300° C.,preferably of 20° C. to 200° C.; at a pressure of 100 Pa to 5·10⁶ Pa;preferably of 1000 Pa to 2·10⁵ Pa; for a time of a few minutes to a fewdays, preferably of one hour to one week.

Advantageously, the solution obtained in step c) d) (step d) is left toage at a temperature of 0° C. to 300° C., preferably of 20° C. to 200°C.; at a pressure of 100 Pa to 5·10⁶ Pa; preferably of 1000 Pa to 2·10⁵Pa; for a time of a few minutes to a few days, preferably of one hour toone week.

Advantageously, the solution S obtained in step f) is left to age at atemperature of 0° C. to 300° C., preferably of 20° C. to 200° C.; at apressure of 100 Pa to 5·10⁶ Pa; preferably of 1000 Pa to 2·10⁵ Pa; for atime of a few minutes to a few days, preferably of one hour to one week.

Advantageously, the solvents are evaporated at a temperature of 0° C. to300° C., preferably of 10° C. to 160° C.; at a relative humidity (RH) of0 to 100%, preferably of 20% to 95%. These evaporation conditions makeit possible in particular to obtain a homogeneous and flexible membranewhich has the required mesoporosity.

In step h), the organic-inorganic hybrid solution may be deposited orimpregnated on a support by means of a method selected from the methodof deposition by centrifugal coating known as spin coating, the methodof deposition by immersion and withdrawal known as dip coating, themethod of deposition by laminar coating known as meniscus coating, themethod of deposition by spraying known as “spray coating”, or the methodof deposition by casting and the method of deposition by evaporation.

The invention will be better understood on reading the description whichnow follows, and which is given by way of illustration and not oflimitation, referring to the attached drawing, in which:

FIG. 1 is a graph which gives small-angle X-ray scattering diagrams formembranes C, D, E and F prepared in the example.

The intensity (in number of counts) is plotted on the ordinate, and 20is plotted on the abscissa.

The curves represent, from top to bottom, the diagrams for membranes F,C, D and E, respectively.

The text below describes a process for preparing, according to theinvention, a conductive organic-inorganic hybrid material in the form ofa membrane having a mesoporous mineral phase whose walls are providedwith polymeric or oligomeric organic chain links bonded to the mineralnetwork; a conductive function is present, for example, in the pores;and a surfactant may also be present in these same pores.

This process comprises the following steps:

Step 1: The synthesis begins with the preparation of the organometallicprecursor A, which will provide the mesoporous network with flexibilityand mechanical strength. Typically a branched or unbranched polymericchain is functionalized with at least two metal alkoxide functions(RO)_(n)M′-polymer-M′(OR)_(n), where M′ is a metalloid or a metal suchas a p metal or a transition metal or else a lanthanide. Examples of M′are Si, Ti, Zr, Al, Sn, Ce, Eu, La, and Gd, and R is an organic group ofalkyl or aryl type.

The polymer is selected for its mechanical properties (structuring andflexibility), its heat resistance properties and its properties ofresistance to the hydrolysis and to the oxidation of the medium of thefuel cell. Typically this polymer may be selected from the polymersdescribed above. These various polymers may include cation exchangegroups: —SO₃M, —PO₃M₂, —COOM or —B(OM)₂ (with M=H, monovalent metalcation, or N⁺R¹ ₄ (with R¹=H, alkyl or aryl); or precursors: SO₂X, COXor PO₃X₂ (X=F, Cl, Br, I or OR (R=alkyl or aryl)). In another model, thevarious polymers may include anion exchange groups: ₋ ⁺NR² ₃X⁻, where Xrepresents an anion such as, for example, F, Cl, Br, I, NO₃, SO₄H or OR,R being an alkyl radical or an aryl radical, and or each R² represents,independently, H, alkyl, aryl, pyridinium, imidazolinium, pyrazolium orsulfonium; it will also be possible to refer to the list given above.

Step 2: This precursor A is diluted in the presence of a metal alkoxideor metal salt B in a liquid medium; and the selection of the solvent orof the solvent mixture is made in dependence on the medium ofmiscibility of the surfactant agent used subsequently, typicallyalcohols, ethers or ketones which are miscible or partially misciblewith water.

To this metallic precursor, a molar amount C of an organometalliccompound containing hydroxyl functions or hydrolyzable functions ofalkoxide type, and non-hydrolyzable or grafted functions, may be addedover the same time as the mixture (A and B). This compound Ccorresponds, for example, to the formula R³ _(x)R⁴ _(y)M″OR_((n−(x+y))),where M″ represents an element from group IV, for example: Si, or to theformula ZR³ _(x)ZR⁴ _(y)M′″OR_((n−(x+y))), where M′″ is a p metal, atransition metal or a lanthanide, for example: Ti, Zr, Ta, Al, Sn, Eu,Ce, La or Gd, where n is the valence of the metal, Z is a complexingfunction of monodentate type, such as acetate, phosphonate or phosphate,or of bidentate type, such as β-diketones and derivatives thereof, andα- or β-hydroxy acids, R³, R⁴, and R are organic substituents of H,alkyl or aryl type. Particularly for R³, these substituents may includecation exchange groups: —SO₃M, —PO₃M₂, —COOM or —B(OM)₂, in which M=H, amonovalent metal cation, or N⁺R¹ ₄ (where each R¹ represents,independently, H, alkyl or aryl); or precursors of cation exchangegroups: SO₂X, COX or PO₃X₂, (X⊂F, Cl, Br, I or OR′ (R′=alkyl or aryl));or anion exchange groups, such as ⁺NR² ₃X⁻, where X represents an anionsuch as, for example, F, Cl, Br, I, NO₃, SO₄H or OR, R being an alkylradical or an aryl radical, and each R² represents, independently, H,alkyl, aryl, pyridinium, imidazolinium, pyrazolium or sulfonium; it willalso be possible to refer to the list given earlier on above.

Step 3: This solution is mixed with a surfactant agent solution whichwill play the part of the templating, texturizing agent. The selectionof the templating agent depends on the desired mesostructure (cubic,hexagonal, lamellar, vermicular, vesicular or bicontinuous), on the sizeof the pores and the walls of this mesostructure; and on itssolubilization with the other compounds of the present invention, namelythe mineral precursors. Use will be made of surfactant-containingtemplating agents, such as alkyltrimethylammonium salts, alkyl phosphatesalts and alkylsulfonate salts; or of acids, such as dibenzoyltartaricacid, maleic acid, or long-chain fatty acids; or of bases, such as ureaand long-chain amines, to construct mesoporous edifices in which thesize of the pores is limited to a few nanometers (1.6 to 10 nm) and thesize of the walls to approximately 1 nm.

To prepare mesoporous phases with a larger pore size (up to 50 nm), usewill be made of phospholipids; doubly hydrophilic copolymers whoseamphiphilicity is generated in situ by interaction with a substrate; oramphiphilic multiblock copolymers comprising at least one hydrophobicblock in combination with at least one hydrophilic block. Among thesepolymers, mention may be made, for example, of Pluronics® based on PEO(poly(ethylene oxide)) and PPO (poly(propylene oxide)), of(EO)_(n)—(PO)_(m)—(EO)_(n) type, copolymers of((EO)_(n)—(PO)_(m))_(x)—NCH₂CH₂N—((EO)_(n)—(PO)_(m))_(x) type(Tetronic®), the class C_(n)(EO)_(m)(OH) (C_(n)=aryl and/or alkyl chain,EO=ethylene oxide chain), for example, Brij®, Triton® Tergitol orIgepal®, and the class (EO)_(m)-sorbitan-C_(n) (Tween®). These variousblocks were also able to be of acrylic nature, PMAc (poly(methacrylicacid)) or PAAC (poly(acrylic acid)), aromatic PS (polystyrene), vinylicPQVP (polyvinylpyridine), PVP (polyvinylpyrrolidone), PVEE (polyvinylether) or other PDMS (polysiloxane) kind. These various blocks may befunctionalized by conductive groups of cation exchange type; orprecursors of cation exchange groups; or anion exchange groups, such as,for example, PSS (poly(styrenesulfonic) acid) or precursors of anionexchange groups, already defined above. The selected structure-directingagent D is dissolved or diluted in an aqueous-alcoholic medium or in anaqueous-based solvent mixture compatible with the medium used to dilutethe metallic precursors A, B and C.

Step 4: This surfactant-containing organic-inorganic hybrid solution issubsequently hydrolyzed in an acidic or basic medium for a specifictime, which may extend from a few hours to several days, depending onthe selection of the metal precursor, at a controlled temperature fromambient to reflux. Particularly in the case of TiO₂ or ZrO₂ precursors,a chelating agent E, such as, typically, acetylacetone or acetic acid orphosphonates, may be introduced in order to control thehydrolysis/condensation of the inorganic network.

Step 5: The membrane is produced by deposition of the organic-inorganichybrid solution and evaporation under controlled pressure, temperatureand humidity (15° C.<T<80° C.). The evaporation conditions are veryimportant for the organization of the surfactant in the liquid medium,and the final formation of the mesoporous network. The membranesobtained are subsequently heat-treated at between 50° C. and 300° C., toeffect consolidation. The surfactant present in the mesopores of themembrane may be removed by a gentle technique, such as, for example,washing in acidic, aqueous-alcoholic medium. A post-reaction to liberateor generate the conductive function bonded to the inorganic network maybe carried out. Typically this type of post-reaction may be:

an oxidation of a mercaptan group (—SH) by hydrogen peroxide in sulfonicacid SO₃H, or

the hydrolysis of a dialkylphosphonate function (RO)₂(O)P— with HCl,directly or via the formation of an intermediate (Me₃SiO)₂(O)P—,followed by hydrolysis with MeOH, to form a phosphonic acid —PO₃H₂.

This post-reaction may also correspond to a grafting of the surfacehydroxyls M-OH of the inorganic network of the membrane with a metalorganoalkoxide. In all of these cases, the membrane is placed in aliquid medium, to allow it to swell and to allow the reactive molecularentities to spread within the pores of the membrane.

In order to avoid any side reaction within the membrane during theoperation of the cell, the proton conductive membrane is purified byvarious oxidizing, acidic (or basic), and aqueous washes, which allowall of the labile organic, organomineral or inorganic entities to beremoved.

In the process according to the invention, the growth of the mesoporousphase containing, integrated in its walls, an oligomer or an organicpolymer is outstandingly controlled in the presence of a templating,texturizing surface active agent. This control is linked in particularto the appropriate choice of the solvents, such as alcohols, ethers, andketones, which are miscible or partially miscible with water, of theprecursors, and of the operating conditions, set out in detail earlieron above.

The membrane may also be prepared in the form of a self-supporting film,using liquid deposition techniques, namely centrifugal coating (spincoating), immersion/withdrawal (dip coating) or laminar coating(meniscus coating). This formed film is subsequently detached from itssupport by swelling in a solvent such as water.

The spraying technique known as spray coating may also be used to formaerosols from the organic-inorganic hybrid solution and so to carry outthe impregnation of the electrodes, so as, in particular, to enhance theelectrode-membrane compatibility on assembly to form the cell.

The invention will now be described by reference to the followingexample, which is given by way of illustration, and not of limitation.

EXAMPLE

In this example a hybrid membrane based on a continuoussilica-poly(propylene oxide) network is prepared.

Tetraethoxysilane (TEOS) and the 3-mercapto-propyltrimethoxysilanecarrying an —SH function, a precursor of an acid group SO₃H, are dilutedin an alcoholic solvent at 3% by mass. The surface-active agent (Brij®30) is subsequently added to the mixture and the solution is hydrolyzedwith 0.2 M hydrochloric acid. A solution of organosilicon-containingpoly(propylene oxide) polymer at a dilution of 3% in the same solvent isadded.

After homogenization and aging of the hybrid solution for 12 hours, thesolution is evaporated in a Petri dish to form a 150 μm homogeneous,flexible membrane.

Three parameters are varied in this preparation:

the [SiO_(2-Ormosil)/polymer_(-SiO) ₂ ] mass ratio

the nature of the alcoholic solvent (ethanol, propanol, methanol andTHF)

the type of functionalization of the silica, SiO₂—SH or SiO₂—SO₂H, bythe addition or non-addition of hydrogen peroxide.

Table 1 gives the various formulations prepared: TABLE 1 Rt_(mass) Molarratio Molar ratio Name SiO₂/polymer (R—Si/TEOS) Solvent (H₂O₂/R—SiO₂) A60% 0.3 C₂H₅OH 0.4 B 50% 0.3 C₂H₅OH 0.4 C 40% 0.3 C₂H₅OH 0.4 D 30% 0.3C₂H₅OH 0.4 E 20% 0.3 C₂H₅OH 0.4 F 0% 0.0 C₂H₅OH 0.4 G 40% 0.3 i-C₃H₇OH0.4 H 40% 0.3 C₄H₆O 0.4 I 40% 0.3 CH₃OH 0.4 J 30% 0.3 C₂H₅OH 0   K 30%0.3 C₂H₅OH 0.4 (reflux) L 30% 0.3 C₂H₅OH 1.1 (reflux)

These various formulations give transparent membranes in all cases.

1) Study of the Silica/Polymer Mass Ratio in the Membrane:

Membranes C to F form self-supporting films and are flexible. Theflexibility of the membranes is ensured for a high silica content ofbetween 30% and 40%. TABLE 2 Characteristics of Name Rt_(mass)SiO₂/polymer the membrane A 60% Brittle membrane B 50% Rigid membrane C40% Semirigid membrane D 30% Flexible membrane E 20% Flexible membrane F0% Flexible membrane

The small-angle X-ray scattering diagrams of these membranes areevidence of a mesoporous organization with a diffraction peak centeredon 11 nm (see FIG. 1, where the curves, from top to bottom, give,respectively, the diagrams for membranes F, C, D and E).

2) Study of the nature of the solvent:

Membranes A and B form self-supporting films which are more flexiblethan membranes C and D. For a high silica content of 40%, a differentflexibility is observed depending on the nature of the solvent, therebyindicating a different macroscopic membrane structure. TABLE 3Characteristics of Name Solvent the membrane C EtOH Semirigid membrane GIPrOH Flexible membrane H THF Rigid membrane I MeOH Rigid membrane

3) Study of the Functionalization of the Silica, SiO₂—SH or SiO₂—SO₃H,by the Addition or Non-Addition of Hydrogen Peroxide:

The addition of hydrogen peroxide to oxidize the SH or SO₃H functionsdoes not lower the flexibility of the membranes. TABLE 3 Molar ratioCharacteristics of Name (H₂O₂/R—SiO₂) the membrane C 0.4 Flexiblemembrane J 0.4 Flexible membrane (reflux) K 1.1 Flexible membrane(reflux)

Table 4 gives the ionic exchange capacity and conductivity values ofthese membranes. TABLE 4 Molar ratio IEC_(assayed) IEC_(theoretical)Conductivity Name (H₂O₂/R—SiO₂) (meq H⁺· g⁻¹) (meq H⁺· g⁻¹) (S · cm⁻¹) C0.4 0.39 1.15 2.26 × 10⁻⁵ J 0.4 0.39 1.15 5.34 × 10⁻⁵ (reflux) K 1.11.05 1.15 5.68 × 10⁻⁴ (reflux)

In the case of a molar fraction of hydrogen peroxide of 0.4, littleionic exchange and a low conductivity are observed. This resultdemonstrates that the oxidation yield of the SH and SO₃H bonds is low.Increasing the amount of hydrogen peroxide by a factor of 3 allows theconductivity to be increased by a factor of 10.

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1-28. (canceled)
 29. A conductive organic-inorganic hybrid materialcomprising a mineral phase in which walls define pores forming astructured mesoporous network with open porosity; said material furthercomprising an organic oligomer or polymer integrated in said walls andbonded covalently to the mineral phase, and optionally another phaseinside the pores, composed of at least one surface active agent; atleast one of the mineral phase, and the organic oligomer or polymerhaving conductive and/or hydrophilic functions.
 30. The material ofclaim 29, wherein the mineral phase has conductive and/or hydrophilicfunctions on the surface of its pores.
 31. The material of claim 29,wherein the organic oligomer or polymer has conductive and/orhydrophilic functions.
 32. The material of claim 29, wherein theoptional phase composed of at least one surface active agent hasconductive and/or hydrophilic functions.
 33. The material of claim 29,wherein said conductive functions are selected from cation exchangegroups.
 34. The material of claim 33, wherein said cation exchangegroups are selected from the following groups: SO₃M; —PO₃M₂; —COOM andB(OM)₂, where M represents hydrogen, a monovalent metal cation, or ⁺NR¹₄, where each R¹, independently, represents a hydrogen, an alkyl radicalor an aryl radical.
 35. The material of claim 29, wherein saidconductive functions are selected from anion exchange groups.
 36. Thematerial of claim 35, wherein said anion exchange groups are selectedfrom the following groups: pyridyl, imidazolyl, pyrazolyl; triazolyl;the radicals of formula ⁺NR² ₃X⁻, where X represents F, Cl, Br, I, NO₃,SO₄H or OR, R being an alkyl radical or an aryl radical, and where eachR², independently, represents a hydrogen, an alkyl radical or an arylradical; and the basic aromatic or nonaromatic radicals containing atleast one radical selected from imidazole, vinylimidazole, pyrazole,oxazole, carbazole, indole, isoindole, dihydrooxazole, isoxazole,thiazole, benzothiazole, isothiazole, benzimidazole, indazole,4,5-dihydropyrazole, 1,2,3-oxadiazole, furazan, 1,2,3-thiadiazole,1,2,4-thiadiazole, 1,2,3-benzotriazole, 1,2,4-triazole, tetrazole,pyrrole, aniline, pyrrolidine, and pyrazole radicals.
 37. The materialof claim 29, wherein the mineral phase is composed of at least one oxideselected from metal oxides, metalloid oxides and mixed oxides thereof.38. The material of claim 37, wherein said oxide is selected from theoxides of silicon, titanium, zirconium, hafnium, aluminum, tantalum,tin, rare earths and mixed oxides thereof.
 39. The material of claim 29,wherein the mesoporous network has an organized structure with arepeating unit.
 40. The material of claim 39, wherein the mesoporousnetwork has a cubic, hexagonal, lamellar, vermicular, vesicular orbicontinuous structure.
 41. The material of claim 29, wherein the sizeof the pores is from 1 to 100 nm.
 42. The material of claim 29, whereinthe organic polymer is a thermally stable polymer.
 43. The material ofclaim 42, wherein the organic polymer is selected from polyetherketones;polysulfones; polyethersulfones; polyphenylethersulfones;styrene/ethylene, styrene/butadiene, and styrene/isoprene copolymers;polyphenylenes; polyimidazoles; polyimides; polyamideimides;polyanilines; polypyrroles; polysulfonamides; polypyrazoles;polyoxazoles; polyethers; poly((meth)acrylic acid)s; polyacrylamides;polyvinyls; acetal resins; polyvinylpyridines; polyvinylpyrrolidones;polyolefins; poly(styrene oxide)s; fluoro resins andpolyperfluorocarbons; poly(vinylidene fluoride)s;polychlorotrifluoroethylenes; polyhexafluoropropenes;perfluoroalkoxides; polyphosphazenes; silicone elastomers; and blockcopolymers comprising at least one block composed of a polymer selectedfrom the above polymers.
 44. The material of claim 29, wherein thesurface active agent is selected from alkyltrimethylammonium salts,alkyl phosphate salts, alkylsulfonate salts, dibenzoyltartaric acid,maleic acid, long chain fatty acids, urea, long chain amines,phospholipids, doubly hydrophilic copolymers whose amphiphilicity isgenerated in situ by interaction with a substrate, and amphiphilicmultiblock copolymers comprising at least one hydrophobic block incombination with at least one hydrophilic block.
 45. A membranecomprising the material of claim 29, optionally deposited on a support.46. An electrode comprising the material of claim
 29. 47. A fuel cellcomprising at least one membrane comprising a conductiveorganic-inorganic hybrid material comprising a mineral phase in whichwalls define pores forming a structured mesoporous network with openporosity; said material further comprising an organic oligomer orpolymer integrated in said walls and bonded covalently to the mineralphase, and optionally another phase inside the pores, composed of atleast one surface active agent; at least one of the mineral phase, andthe organic oligomer or polymer having conductive and/or hydrophilicfunctions, said membrane optionally deposited on a support; and/or atleast one electrode comprising a conductive organic-inorganic hybridmaterial comprising a mineral phase in which walls define pores forminga structured mesoporous network with open porosity; said materialfurther comprising an organic oligomer or polymer integrated in saidwalls and bonded covalently to the mineral phase, and optionally anotherphase inside the pores, composed of at least one surface active agent;at least one of the mineral phase, and the organic oligomer or polymerhaving conductive and/or hydrophilic functions.
 48. A process forpreparing the material of claim 29, comprising the following steps:a)—synthesizing a precursor compound A, composed of an organic oligomeror polymer which carries precursor functions of the mesoporous mineralphase, and preparing an organic-inorganic hybrid solution in a solventof said precursor compound A; b)—hydrolyzing the organic-inorganichybrid solution obtained in step a) and allowing the solution to age;c)—diluting the hydrolyzed and aged organic-inorganic hybrid solution ofthe precursor compound A, obtained in step b), in a solvent of a mineralprecursor B intended to constitute the mesoporous mineral phase, wherebya new organic-inorganic hybrid solution is obtained; d)—hydrolyzing theorganic-inorganic hybrid solution obtained in step c) and allowing thesolution to age; e)—preparing a solution, in a solvent, of a surfaceactive agent D, a templating, texturizing, agent for the mesoporousmineral phase; f)—mixing the solution obtained in step c) with thesolution obtained in step e) to give a solution S; g)—optionally,hydrolyzing the solution S obtained in step f) and allowing the solutionS to age; h)—depositing or impregnating the hydrolyzed and aged hybridsolution S on a support; i)—evaporating solvents under controlledpressure, temperature, and humidity conditions; j)—carrying out a heattreatment to consolidate the material; k)—optionally removing thesurface active agent D completely or partially; l)—optionally separatingor removing the support.
 49. The process of claim 48, whereinadditionally a chelating agent E is added to the solution S obtained instep f).
 50. The process of claim 48, wherein, during step c), to thesolution based on the organomineral precursor A, a compound C is furtheradded which carries, on the one hand, conductive and/or hydrophilicfunctions and/or precursor functions of conductive and/or hydrophilicfunctions, and, on the other hand, functions capable of undergoingbonding to the surface of the pores of the mesoporous network.
 51. Theprocess of claim 48, wherein the process further comprises a final stepof treatment to liberate or generate conductive and/or hydrophilicfunctions on the surface of the pores of the material.
 52. The processof claim 48, wherein the organic-inorganic hybrid solution obtained instep a) is left to age at a temperature of 0 to 300° C.; at a pressureof 100 Pa to 5·10⁶ Pa; for a time of a few minutes to a few days. 53.The process of claim 48, wherein the organic-inorganic hybrid solutionobtained in step c) is left to age at a temperature of 0° C. to 300° C.;at a pressure of 100 Pa to 5·10⁶ Pa; for a time of a few minutes toseveral days.
 54. The process of claim 48, wherein the solution Sobtained in step f) is left to age at a temperature of 0° C. to 300° C.;at a pressure of 100 Pa to 5·10⁶ Pa; for a time of a few minutes to afew days.
 55. The process of claim 48, wherein the solvents areevaporated at a temperature of 0 to 300° C.; at a relative humidity (RH)of 0 to 100%.
 56. The process of claim 48, wherein, in step h), theorganic-inorganic hybrid solution is deposited or impregnated on asupport by a method selected from the method of deposition bycentrifugal coating known as spin coating, the method of deposition byimmersion and withdrawal known as dip coating, the method of depositionby laminar coating known as meniscus coating, the method of depositionby spraying known as “spray coating”, the method of deposition bycasting and the method of deposition by evaporation.
 57. The material ofclaim 37, wherein said oxide is selected from the oxides of europium,cerium, lanthanum, and gadolinium, and mixed oxides thereof.
 58. Thematerial of claim 29, wherein the size of the pores is from 1 to 50 nm.59. The process of claim 48, wherein the organic-inorganic hybridsolution obtained in step a) is left to age at a temperature of 20° C.to 200° C.; at a pressure of 1000 Pa to 2·10⁵ Pa; for a time of one hourto one week.
 60. The process of claim 48, wherein the organic-inorganichybrid solution obtained in step c) is left to age at a temperature of20° C. to 200° C.; at a pressure of 1000 Pa to 2·10⁵ Pa; for a time ofone hour to one week.
 61. The process of claim 48, wherein the solutionS obtained in step f) is left to age at a temperature of 20° C. to 200°C.; at a pressure of 1000 Pa to 2·10⁵ Pa; for a time of one hour to oneweek.
 62. The process of claim 48, wherein the solvents are evaporatedat a temperature of 10° C. to 160° C.; at a relative humidity (RH) of20% to 95%.